Clear tmthing at tic end

Causes [rare?] crash when changing levels. Thanks to @WalesGaming of
Twitter for reporting this!

src/g_game.c

@@ -658,7 +658,7 @@ boolean G_Responder(event_t *ev)
                  && ev->data1 != KEY_NUMLOCK
                  && (ev->data1 < KEY_F1 || ev->data1 > KEY_F12))
                      || (ev->type == ev_mouse
-                         && (ev->data1 && !(ev->data1 & MOUSE_WHEELUP || ev->data1 & MOUSE_WHEELDOWN)))
+                         && (ev->data1 && !(ev->data1 & (MOUSE_WHEELUP | MOUSE_WHEELDOWN))))
                              || (ev->type == ev_gamepad
                                  && gamepadwait < I_GetTime()
                                  && gamepadbuttons
@@ -812,11 +812,15 @@ void G_Ticker(void)
     int         buf;
     ticcmd_t    *cmd;
 
+    P_MapStart();
+
     // do player reborns if needed
     for (i = 0; i < MAXPLAYERS; i++)
         if (playeringame[i] && players[i].playerstate == PST_REBORN)
             G_DoReborn(i);
 
+    P_MapEnd();
+
     // do things to change the game state
     while (gameaction != ga_nothing)
     {
@@ -1549,12 +1553,16 @@ void G_DoLoadGame(void)
 
     leveltime = savedleveltime;
 
+    P_MapStart();
+
     // dearchive all the modifications
     P_UnArchivePlayers();
     P_UnArchiveWorld();
     P_UnArchiveThinkers();
     P_UnArchiveSpecials();
 
+    P_MapEnd();
+
     if (!P_ReadSaveGameEOF())
         I_Error("Bad savegame");
 

src/p_local.h

@@ -242,6 +242,9 @@ void P_RadiusAttack(mobj_t *spot, mobj_t *source, int damage);
 
 void P_ApplyTorque(mobj_t *mo); // killough 9/12/98
 
+void P_MapStart(void);
+void P_MapEnd(void);
+
 //
 // P_SETUP
 //

src/p_map.c

@@ -32,6 +32,7 @@ along with DOOM RETRO. If not, see http://www.gnu.org/licenses/.
 #include <stdlib.h>
 
 #include "doomstat.h"
+#include "i_system.h"
 #include "m_bbox.h"
 #include "m_random.h"
 #include "p_local.h"
@@ -2057,3 +2058,18 @@ void P_CreateSecNodeList(mobj_t *thing, fixed_t x, fixed_t y)
         tmbbox[BOXLEFT] = tmx - tmthing->radius;
     }
 }
+
+// cphipps 2004/08/30 -
+// Must clear tmthing at tic end, as it might contain a pointer to a removed
+// thinker, or the level might have ended/been ended and we clear the objects it
+// was pointing to. Hopefully we don't need to carry this between tics for sync.
+void P_MapStart(void)
+{
+    if (tmthing)
+        I_Error("P_MapStart: tmthing set!");
+}
+
+void P_MapEnd(void)
+{
+    tmthing = NULL;
+}

src/p_setup.c

@@ -1103,6 +1103,8 @@ void P_SetupLevel(int episode, int map)
     bloodSplatQueueSlot = 0;
     memset(bloodSplatQueue, 0, sizeof(mobj_t *) * bloodsplats);
 
+    P_MapStart();
+
     P_LoadThings(lumpnum + ML_THINGS);
 
     P_InitCards(&players[0]);
@@ -1124,6 +1126,8 @@ void P_SetupLevel(int episode, int map)
     // set up world state
     P_SpawnSpecials();
 
+    P_MapEnd();
+
     // preload graphics
     R_PrecacheLevel();
 }

src/p_tick.c

@@ -106,17 +106,22 @@ void P_Ticker(void)
         return;
 
     // pause if in menu and at least one tic has been run
-    if (!netgame && menuactive  && players[consoleplayer].viewz != 1)
+    if (!netgame && menuactive && players[consoleplayer].viewz != 1)
         return;
 
-    for (i = 0; i < MAXPLAYERS; i++)
-        if (playeringame[i])
-            P_PlayerThink(&players[i]);
+    P_MapStart();
+
+    if (gamestate == GS_LEVEL)
+        for (i = 0; i < MAXPLAYERS; i++)
+            if (playeringame[i])
+                P_PlayerThink(&players[i]);
 
     P_RunThinkers();
     P_UpdateSpecials();
     P_RespawnSpecials();
 
+    P_MapEnd();
+
     // for par times
     leveltime++;
 }